Printed indicia which are applied to T-shirts and other articles of clothing have become very popular in the last decade. Boutiques which specialize in printing fanciful indicia such as ornamentation, slogans, college names, or sports team names on T-shirts and other clothing are commonly seen in shopping malls. The indicia available at these boutiques can be pre-printed on a substrate and applied to articles of clothing purchased by the consumer with a heated press by boutique operators, or can be applied directly to an article of clothing. The indicia can comprise either simple one-color block letters or elaborate multi-color illustrations.
In common use in the industry in printing objects such as substrates or articles of clothing is a multi-station, turret type, printing press. The printing press of this type has a plurality of flat beds or platens spaced along its perimeter. Corresponding to each of these beds is a series of stations where a part of the indicia is alternately printed and cured on the object, i.e., substrate or article, being printed. The number of stations employed depends on the number of colors to be printed on the object. Indicia can consist of up to ten colors or more.
Also in common use are single station printing machines. Single station machines require the operator to print one color at a time using one screen at a time. After one color is printed on an object, the screen is removed and another screen placed thereon to print another color. As with the multi-station press, the new screen must be perfectly aligned with the preceding screen such that the image remains in registration. This single-stage process is very time-consuming, especially if multiple colors are used.
In using either the single or multi-station presses, the indicia or design is formed in the screen by a conventional process. The screen has an emulsion, which covers some of the interstices in the screen, and other places which are open so ink of a particular color may be deposited onto the object to be printed in the pattern defined by the open or uncovered area. For each color, a different stencilled screen is desired with a different pattern.
To print, the stencil screen embodying the indicia is placed over the object. Ink of the type well-known in the industry for making transfers is flooded onto the screen. After the ink is flooded onto the screen, the ink is squeegeed through the screen onto the object leaving ink of the desired color in the pattern defined by the open interstices in the screen. The squeegee is of any type well-known in the art.
After the excess ink is squeegeed from the screen, the ink is then dried or cured onto the object to be printed. Depending on the type of ink used, the ink is either cured on the object by heating it to a critical temperature, or simply by letting it dry if ink containing solvents is used. Heat is commonly applied by an energy source directed toward the object. The above process is repeated for every color to be contained in the indicia.
The most critical and time-consuming part of the screen printing process involving multiple colors is the alignment or registration of successive screens. Each screen for each color must be in registration with the other screens to ensure that the various colors do not overlap or are incorrectly spaced. Otherwise, the printed indicia will not be in registration, resulting in a skewed or imperfect indicia. Presently, screens are aligned in registration manually, requiring a skilled operator to properly align the screens. However, even with a highly skilled operator the set-up time for screens can take fifteen minutes or more. An unskilled operator takes even longer. Manual registration of screens is well-known in the art.
A screen is manually set in registration by lining up fiducial lines etched in the screen itself or on the screen frame with fiducial lines on the object or on the press itself. Use of fiducial lines is well-known in the art. Due to the parallax experienced when an operator views successive screens from different angles, the screens may be out of registration even with a highly skilled operator. Oftentimes, several pieces are printed to determine if each screen is in registration. If the screens are out of registration, the entire screen alignment process must be redone, and any prints made therefrom must be scrapped. This obviously results in increased down time and production costs, and reduced productivity.